Since the main function of the esophagus and ureter is of mechanic nature, i.e. the propulsion of a solid or a liquid bolus, a characterization of their mechanical behavior is helpful in understanding how these organs function, how pathologic conditions alter their behavior and what possible corrective measures may be usefully employed. Our present objective is to define the length-tension-velocity relationships of the muscles of these organs and determine how the behavior of the single muscle fibers affects the behavior of the whole organ, in vivo and in vitro. Since both longitudianl and circular muscles play a role in peristaltic transport, the bidimensional characteristics of esophagus and ureter will be studied.